My Wife & I have a Burley steel tandem. It's a road tandem with 26" wheels. It's not high proformance in any way, just a good solid touring bike. We have done several tandem rallys & even loaded the racks with groceries.
For us it's about hanging out together on a bike.
We live & ride in a hilly area. I feel brifters or indexed barends are a must to make a tandem enjoyable. With a tandem being able to keep your momentum when changing gears is a must.
For flat terrain or path riding an older non- index shifting bike would be fine.
These are my experiances.